Conventional wisdom once had it that each brain region is responsible for a specific task. And so we have the motor cortex for handling movements, and the visual cortex, for processing sight. And scientists thought that such regions remained fixed for those tasks beyond the age of three.

But within the past decade researchers have realized that some brain regions can pinch hit for other regions, for example, after a damaging stroke.

And now new research finds that the visual cortex is constantly doing double duty—it has a role in processing not just sight, but sound. When we hear [siren sound], we see a siren.

In the study, scientists scanned the brains of blindfolded participants as the subjects listened to three sounds: [audio of birds, audio of traffic, audio of a talking crowd.]
And the scientists could tell what specific sounds the subjects were hearing just by analyzing the brain activity in the visual cortex. [Petra Vetter, Fraser W. Smith and Lars Muckli, Decoding Sound and Imagery Content in Early Visual Cortex, in Current Biology]

The next step is to determine why the visual cortex is horning in on the audio action. The researchers think the additional role conferred an evolutionary advantage: having a visual system primed by sound to see the source of that sound could have given humans an extra step in the race for survival.

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